In practice, gas separation (particularly CO2 separation, for instance for CO2/H2 separation or with natural gas treatment) is carried out at high pressure, by using absorption liquids. Such processes are based on absorption under high pressure, followed by desorption at low pressure. In the desorption step, the gas bubbles spontaneously from the absorption liquid. Usually, the gas then needs to be recompressed for the benefit of the follow-up processes. This is energetically undesirable. In order to then bring the absorption liquid to the absorption pressure, recompression of the liquid is necessary, which is also energetically undesirable. In addition, due to the low pressure, the equipment for the desorption process usually needs to have the same size as the equipment for the absorption process. The absorption and desorption steps are carried out in separate devices, so that the investment costs are high. To sum up, the known high-pressure absorption processes have energetic drawbacks, they are sizable and result in high investment costs. This makes them unsuitable for, for instance, small-scale gas treatment applications, such as for instance fuel cells.